MEMS PARAMETER IDENTIFICATION USING MODULATED WAVEFORMS

• US 20150027198A1
• Filed: 07/23/2013
• Published: 01/29/2015
• Est. Priority Date: 07/23/2013
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Sessego, Raimondo P., Dar, Tehmoor M., Debeurre, Bruno J.
• Granted Patent: US 9,335,340 B2
• Time in Patent Office: Days
• US Class Current: 73/1.37
• CPC Class Codes: B81B 3/0021 Transducers for transforming electrical into mechanical energy or vice versa dynamo-electric machines H02K99/00; electrostatic machines H02N1/00; piezoelectric devices H10N30/00
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 2015/0834 the mass constituting a pendulum having the pivot axis disposed symmetrically between the longitudinal ends, the center of mass being shifted away from the plane of the pendulum which includes the pivot axis
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

A sensor system includes a microelectromechanical systems (MEMS) sensor, control circuit, signal evaluation circuitry, a digital to analog converter, signal filters, an amplifier, demodulation circuitry and memory. The system is configured to generate high and low-frequency signals, combine them, and provide the combined input signal to a MEMS sensor. The MEMS sensor is configured to provide a modulated output signal that is a function of the combined signal. The system is configured to demodulate and filter the modulated output signal, compare the demodulated, filtered signal with the input signal to determine amplitude and phase differences, and determine, based on the amplitude and phase differences, various parameters of the MEMS sensor. A method for determining MEMS sensor parameters is also provided.

Claims

1. A microelectromechanical systems (MEMS) system comprising:

a MEMS sensor having a moveable mechanical element configured to be moveable responsive to an electromagnetic signal applied to the moveable mechanical element, and further comprising a sense contact configured to provide as an output an electromagnetic output signal corresponding to motion of the moveable mechanical element;

a control circuit in electrical communication with the moveable mechanical element of the MEMS sensor, and configured to provide an electromagnetic input signal comprising at least two oscillating frequencies to the moveable mechanical element of the MEMS sensor; and

demodulation circuitry in electrical communication with the sense contact of the MEMS sensor and the control circuit, and configured to demodulate the electromagnetic output signal corresponding to motion of the moveable mechanical element and provide a demodulated signal to the control circuit, wherein the control circuit is configured to evaluate the demodulated signal to determine at least one characteristic of the MEMS sensor.

2. A MEMS parameter identification system as claimed in claim 1 further comprising signal evaluation circuitry in electrical communication with the demodulation circuitry and the control circuit, wherein the signal evaluation circuitry is configured to receive the electromagnetic input signal from the control circuit and the demodulated signal from the demodulator, compare at least one characteristic of the electromagnetic input signal and demodulated signal, and provide a characteristic signal indicative of the compared characteristic to the control circuit.

3. A MEMS parameter identification system as claimed in claim 2 wherein the at least one characteristic is at least one of a phase and amplitude.

4. A MEMS parameter identification system as claimed in claim 1 further comprising digital to analog conversion circuitry electrically coupled to the control circuit and the MEMS sensor, wherein the electromagnetic input signal generated by the control circuit is a digital signal, and wherein the digital to analog conversion circuitry is configured to convert the digital signal to an analog signal and provide it as an analog electromagnetic input signal to the MEMS sensor.

5. A MEMS parameter identification system as claimed in claim 2, further comprising a first signal filter in electrical communication with the control circuit and electrically coupled to the signal evaluation circuitry, wherein the electromagnetic input signal provided by the control circuit comprises at least one lower-frequency signal and one higher-frequency signal, and wherein the first signal filter is configured to remove the higher-frequency signal from the electromagnetic input signal and provide the filtered lower-frequency signal to the signal evaluation circuitry.

6. A MEMS parameter identification system as claimed in claim 5, further comprising a second signal filter electrically coupled to the demodulation circuitry and the signal evaluation circuitry, wherein the demodulated signal provided by the demodulation circuitry comprises at least one lower-frequency signal and one higher-frequency signal wherein the second signal filter is configured to remove higher-frequency signal from the demodulated signal and provide the resulting filtered demodulated lower-frequency signal to the signal evaluation circuitry.

7. A MEMS parameter identification system as claimed in claim 6, further comprising amplification circuitry electrically coupled to the MEMS sensor and the demodulation circuitry, wherein the amplification circuitry is configured to amplify the electromagnetic output signal provided at the sense contact and provide the amplified electromagnetic output signal to the demodulation circuitry.

8. A MEMS parameter identification system as claimed in claim 1, wherein the control circuit further comprises memory storing code, wherein said code, when executed by the control circuit, generates the input signal, evaluates the demodulated signal, and determines at least one MEMS characteristic using the demodulated signal.

9. A MEMS parameter identification system as claimed in claim 2, wherein the control circuit further comprises memory storing code, wherein said code, when executed by the control circuit, generates the input signal, evaluates the characteristic signal, and determines at least one MEMS characteristic using the characteristic signal.

10. A MEMS parameter identification system as claimed in claim 1, wherein the at least two oscillating frequencies comprise a first lower-frequency and a second higher-frequency, and wherein the first lower-frequency is a frequency that causes the moveable mechanical element to physically oscillate responsive to the first lower frequency, and wherein the second higher frequency is a frequency that does not cause the moveable mechanical element to physically oscillate.

11. A MEMS parameter identification system as claimed in claim 10, wherein the first lower-frequency is a frequency between 1 kHz and 10 kHz, and wherein the second higher frequency is a frequency greater than 500 kHz.

12. A microelectromechanical systems (MEMS) application module comprising:

a MEMS sensor having a moveable mechanical element configured to be capable of modulation responsive to an electromagnetic signal applied to the moveable mechanical element, and further comprising a sense contact configured to provide as an output an electromagnetic output signal corresponding to motion of the moveable mechanical element;

a control circuit in electrical communication with the moveable mechanical element of the MEMS sensor, and configured to provide an electromagnetic input signal comprising a first low-frequency component of a frequency low enough to cause the moveable mechanical element to physically oscillate, and a second high-frequency component of a frequency high enough to not cause oscillation in the moveable mechanical element;

demodulation circuitry in electrical communication with the sense contact of the MEMS sensor, and configured to demodulate the electromagnetic output signal corresponding to motion of the moveable mechanical element to remove the carrier component, and provide a demodulated signal as a demodulated output;

a first signal filter in electrical communication with the control circuit, wherein the first signal filter is configured to receive the electromagnetic input signal, remove the higher-frequency signal from the electromagnetic input signal, and provide the filtered lower-frequency signal as an output;

a second signal filter electrically coupled to the demodulation circuitry, wherein the demodulated signal provided by the demodulation circuitry comprises at least one lower-frequency signal and one higher-frequency signal, and wherein the second signal filter is configured to remove the higher-frequency signal from the demodulated signal and provide the resulting filtered demodulated lower-frequency signal as an output;

signal evaluation circuitry electrically coupled to the first signal filter and second signal filter and the control circuit, wherein the signal evaluation circuitry is configured to receive the filtered lower-frequency signal from the first signal filter and filtered demodulated lower-frequency signal from the second signal filter, compare at least one characteristic of those signals, and provide a characteristic signal indicative of the at least one compared characteristic to the control circuit.

13. The MEMS application module as claimed in claim 12 further comprising:

capacitance to voltage conversion circuitry electrically coupled to a sense contact and configured to convert an electromagnetic output signal to a voltage and provide the voltage as a voltage output; and

analog to digital conversion circuitry electrically coupled to the voltage conversion circuitry and in electrical communication with the control circuit, wherein the analog to digital conversion circuitry is configured to convert the voltage output to a digital output and provide it to the control circuit, and wherein the control circuit is further configured to monitor the digital output and, based on the digital output, to determine at least one of a change in motion of the MEMS application module or change in forces applied to the MEMS application module.

14. A MEMS parameter identification system as claimed in claim 12, wherein the first lower-frequency of the electromagnetic input signal is a frequency that causes the moveable mechanical element to physically oscillate responsive to the first lower frequency, and wherein the second higher frequency of the electromagnetic input signal is a frequency that does not cause the moveable mechanical element to physically oscillate.

15. A method of determining a parameter of a MEMS sensors in a system, comprising:

generating an input signal including at least one high-frequency component selected to not cause physical oscillation of a moveable mechanical element of a MEMS sensor, and one low-frequency component selected to cause physical oscillation of a moveable mechanical element of a MEMS sensor;

providing the input signal to a MEMS sensor comprising at least one moveable mechanical element to cause a modulated output signal comprising high and low frequency components to be provided from the MEMS sensor;

de-modulating the modulated output signal provided by the MEMS sensor;

filtering the de-modulated output signal to remove the high frequency components; and

,

evaluating the de-modulated, filtered signal to determine at least one characteristic of the MEMS sensor.

16. A method as claimed in claim 15, wherein the step of evaluating the de-modulated output signal further includes the step of comparing the de-modulated, filtered signal to the input signal to determine at least one difference between the signals.

17. A method as claimed in claim 16, wherein the at least one determined difference includes at least one of amplitude and phase differences.

18. A method as claimed in claim 17, further including the step of utilizing the at least one characteristic of the MEMS sensor to update at least one of a compensation or calibration parameter for the MEMS sensor.

19. A method as claimed in claim 15, wherein the steps are performed in an application module configured to perform functions other than exclusively testing using an output from a MEMS sensor mounted in the application module, and wherein the module is configured to use output from the MEMS sensor to determine a function performed by the application module.

20. A method as claimed in claim 15, wherein the steps are performed in equipment configured to temporarily electrically couple to a various MEMS sensor for purposes of testing the MEMS sensors.